MIDDLETON, Idaho (AP) - Officials at Middleton Heights Elementary didn't set out to confront gender stereotypes when they started splitting up the boys and girls.

But that's exactly what happened, with the rural Idaho public school now among dozens nationwide being targeted by the American Civil Liberties Union in a bitter struggle over whether single-sex learning should be continued.

While the Middleton school is believed to be alone in offering single-sex classes in Idaho, the movement is widespread.

Single-sex classes began proliferating after the federal government relaxed restrictions in 2006. With research showing boys are graduating at lower rates than girls and faring worse on tests, plenty of schools were paying attention.

An estimated 500 public schools nationwide offer some all-boy and all-girl classrooms, up from a handful in 2002.

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